1. Field of the Invention
The present invention relates to a method for producing a silicon epitaxial wafer with a buried diffusion layer in which an impurity is ion-implanted, and an epitaxial wafer with a buried diffusion layer, and more particularly, to a case that Sb is implanted as the impurity.
2. Description of the Related Art
Techniques for obtaining a silicon epitaxial wafer for a device such as a bipolar device, a BiCMOS device, and a power IC are commonly known. Such a wafer is obtained, for example, by diffusing an impurity in a silicon single crystal wafer obtained from a silicon single crystal ingot produced by the Czochralski method, or the floating zone method to form a p- or n-type diffusion layer, and growing a silicon epitaxial layer on the diffusion layer by vapor-phase epitaxy. For example, Japanese Unexamined Patent Application Publication No. H05-183046 discloses an example of a method for forming a buried diffusion layer.
Hereinafter, a conventional method for producing a silicon epitaxial wafer with a buried diffusion layer is explained in detail.
First, an oxide film is formed on a silicon single crystal wafer, for example, by thermal oxidation. On the oxide film, a mask pattern is formed by photolithography.
Next, for example, an n-type impurity is implanted into the wafer by ion implantation method. The impurity is diffused to form a diffusion layer. At the time of diffusing the implanted impurity to form a diffusion layer, the wafer is annealed. This anneal also provides an oxide film on the diffusion layer.
Then, the oxide film formed on the wafer (the oxide film portion that was covered by the mask and the oxide film on the diffusion layer) is removed by etching with hydrofluoric acid. Furthermore, the wafer is cleaned with the SC-1 solution (ammonia and aqueous hydrogen peroxide) and so on, and then the wafer is dried.
After that, on the silicon wafer with the buried diffusion layer, a silicon epitaxial layer is formed, for example, by vapor-phase epitaxy. In this way, the diffusion layer is buried.
As mentioned above, a silicon epitaxial wafer with a buried diffusion layer (an epitaxial wafer with a buried diffusion layer) is obtained.
However, when an epitaxial layer is formed, for example, on a wafer into which Sb is implanted at a high dose of 1.0×1016 ions/cm2 or more by the conventional production method, crystal defects tend to generate where Sb is implanted. Accordingly, crystal defects often generate or many crystal defects generate in the epitaxial layer.
The crystal defects in the epitaxial layer generate even when the wafer undergoes a heat treatment (oxidation) for restoring crystallinity after the Sb implantation. After all, generation of the crystal defects cannot be prevented.
The generation of the crystal defects depends on Sb dose to be implanted. When Sb dose lowers, generation of the crystal defects is reduced. Therefore, there have conventionally been no other choice but to implant Sb at a dose of 1.0×1016 ions/cm2 or less in view of generation of the crystal defects. Consequently, it has been difficult to obtain an epitaxial wafer in which generation of crystal defects is reduced and Sb is implanted at a high dose.